Since the early 1990's, aneurysm coils have been made of smooth, platinum wire. More recently, aneurysm coils have become available that are coated with a hydrogel material or have a PGLA suture within the coil, both of these alterations designed to help aneurysms heal. The surfaces of these coils, however, remain smooth and otherwise unmodified.
An aneurysm can be described as a bulging of a vessel wall generally caused by blood pressure acting on a weakened portion of the vessel wall. When the wall of a vessel has a weakness, the blood pressure can dilate or expand the region of the vessel at the point of weakness to form a “sac”, also called a “berry” or “saccular aneurysm,” shown as element 10 in FIG. 1. The pressure of an aneurysm against surrounding tissues can cause pain and tissue damage. The blood in the vicinity of the aneurysm can become turbulent, leading to the formation of blood clots, which may be carried to various body organs where they may cause various complications, including cerebrovascular incidents, myocardial infarctions and pulmonary embolisms. Should an aneurysm rupture and begin to leak blood (causing a subarachnoid hemorrhage), the condition can become life threatening within minutes.
There are various methods currently available in the art to treat aneurysms. Coil embolization is one such method which is commonly used to treat aneurysms and in many cases is considered safer for the patient than open craniotomy. In current techniques, aneurysm coils take the form of spiral-wound wires having a circular cross-section that can assume a more complex overall three dimensional shape after insertion into the aneurysm. By using a material which is highly flexible and relatively small in diameter, the coil can be installed in a catheter or micro-catheter in a relatively linear configuration and assume a more complex shape after being pushed from the distal end of the catheter using a pusher. The vascular embolization procedure typically requires the surgeon to advance a micro-catheter to a location within the aneurysm or proximal to the opening of the aneurysm. Thereafter, a biologically-compatible coil may be pushed through the catheter such that the coil is “packed” within the aneurysm such that blood flow is partially or completely blocked from flow into the aneurysm. The presence of the coil inside the aneurysm is meant to encourage clot and scar formation inside the aneurysm, and eventually growth of the lining of the blood vessel (the endothelium) across the opening of the aneurysm which protects the aneurysm from rupturing.
A problem in the field of endovascular therapy for aneurysms is the incidence of aneurysm recurrence and re-growth. Typically, aneurysm coils may fill less that fifty percent of the total volume of the aneurysm. Although this amount of filling is usually adequate to promote a decrease in blood flow initially, with time, pressure and the pulsatile flow of blood often results in the device becoming repositioned or compacted within the aneurysm, thereby forming cavities or areas that can result in recurrent aneurysm formation. The ability for blood to flow into the aneurysm in this way despite the presence of a coil can lead to recannalization of the aneurysm with significant consequences such as rupture or tearing of the wall of the aneurysm. It is thus an advantage of one or more embodiments of the current invention to reduce the likelihood of such repositioning and/or compaction of the coil by providing a coil which encourages cellular adhesion and tissue growth on the surface of the coil, thus improving the likelihood of anchoring the coil within the aneurysm space, promoting complete filling of the aneurysm with fibrous tissue and leading to growth of endothelial cells across the opening of the aneurysm sealing off the aneurysm from the vascular system and thereby protecting the aneurysm from bleeding.
As noted above, prior art coils are known. For example, Ferrera et al. (US 2003/0199887) and Jones et al. (US 2003/0004531) disclose a porous or textural embolization devices, and Lorenzo et al. (US 2006/0200190) discloses either one or two wires which are helically wound to form a coil. Attempts also have been made to coat coils with a growth-promoting composition. For example, Greene et al (U.S. Pat. No. 6,299,619) discloses a device which can carry hydrogel, drugs or other bioactive materials to stabilize or reinforce the aneurysm. Another treatment disclosed in Evans et al. (U.S. Pat. No. 6,335,384) comprises catheter delivery of platinum microcoils into the aneurysm cavity in conjunction with an embolizing composition comprising a biocompatible polymer and solvent. The deposited coils or other non-particulate agents are said to act as a lattice about which a polymer precipitate grows thereby embolizing the blood vessel. The wires used in forming these prior art coils are typically of the standard round shape having a circular cross section, with a particular diameter specified, or with respect to Lorenzo et al., utilize a helically twisted or wound wire. As is illustrated in the scanning electron micrographs of FIGS. 4-6, the extent of cellular growth along the surface of prior art coils, such as those having a circular cross section, is not optimized for endothelial growth.
Aneurysm coils should not only occupy as much of the volume of the aneurysm as possible and encourage the growth of fibrous tissue and endothelium as described above, they should also have other desirable properties including softness and predictable folding characteristics. Aneurysms are by their very nature thin walled structures that are prone to rupture. As a result, aneurysm coils should be soft, pliant and fold in ways that do not put undue pressure on the walls of the aneurysm. For instance, if an aneurysm coil is too stiff, then when it emerges from the catheter it may be prone to pierce the wall of the aneurysm and cause a hemorrhage in the brain. If the coil folds in a way that creates a sharp or acute angle, this acute angle may likewise be prone to put undesired focal pressure on the wall of the aneurysm, at the risk of rupturing it and causing hemorrhage. Thus, any design of an aneurysm coil must engender both softness and predictable bendability with non-sharp or non-acute angles to avoid dangerous pressure on the walls of the aneurysm.
The delivery mechanics of many of these prior art aneurysm treatment methods can therefore be difficult and complicated due, in part, to i) the problems associated with deploying such coils and ii) the inherent nature of introducing foreign substances in vivo. As such, there is a need in the art for a simple and inexpensive coil design with predictable packing characteristics and is also effective at promoting cellular adhesion and tissue growth along the coil. Such a coil design is believed to result in anchoring the coil within the aneurysm to effectively eliminate blood flow therein, and providing a substrate for endothelium to grow across the opening of the aneurysm sealing it off from the flow of blood in the vessel.
Accordingly, one or more embodiments of the present invention may utilize an aneurysm coil comprising a single primary wire having a non-circular cross-sectional shape which may provide enhanced cellular adhesion and tissue growth along the coil surface when compared to coils employing wire having a circular cross-sectional area or coils employing two or more wires. Further, the single wire of non-circular cross section when formed into a coil may not only provide improved cellular adhesion, but also constitute a soft, non traumatic intra-aneurysmal device having the desirable properties noted above with more predictable bending and folding characteristics thereby improving the safety of using the device and placing it into the aneurysm.
The following patents, applications and publications as listed below and throughout this document are hereby incorporated by reference in their entirety herein.
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